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Cognitive Neuroscience Lecture 13: Spatial Representation
L13: Spatial Representation What is the problem to be solved? Need to know where things are so that: - Identification: move our eyes to them o ID what it is; face/word/unfamiliar - Action: interact with objs o Pick up, sit on them, avoid them, etc. - Navigation: find them when they are outside the range of our senses o Your house, your car, supermarket o o What: STGàIFG (superior temporal gyrus to inferior frontal gyrus) o Where: STGàSPLàSFG (STGàsup. Parietal lobeàsuperior frontal gyrus) - Visual pathways: o Superior longitudinal fasciculusàPosteroparietal cortex o Inferior longitudinal fasciculusàinferior temporal cortex Representation of location Relative by reference to something else: reference point ''' Anything can be a reference point Reference point is a defining aspect of a '''frame of reference What reference frames used by brain areas that encode locations? - Cells in v1? - Cells in the doral/parietal (where) pathway? Reference frames: - Retino-centered - Viewer-centered (ego centric) - Object-centered (allo-centric) Frame of reference for V1 neurons - Calcarine fissure (v1) - Fovea most posterior - In goes out, up goes down, left goes right - V1 neurons only encode in terms of direction and distance from fixation o Retino-centric frame of reference (relative to fixation) - We know this because: o Objects in world that stim same location in retina represented by same v1 neurons § If a cup is at point A on retina, and then a phone is at point A, these will both activate same v1 neurons o When fixation moves, same objs represented by diff v1 neurons (ie not obj centric) Cortical blindness - Deficit defined relative to fixation - When fixation moves, same location in external space represented differently Frames of reference: evidence from visuo-spatial neglect Visuo-spatial neglect/extinction - Difficulty in perceiving/attending/being conscious of stim on contralesional side of space Varieties: - Viewer centered - Object centered Provides evidence for viewer-centered and object-centered frames of reference in temporal/parietal areas Neuropsychological cases: right temporal/parietal subsequent to drug overdose Line bisection: better for shorter line Line cancellation: cross out all lines on page Frames of reference: evidence from visuospatial neglect ' - Not cortical blindness; V1 is intact - Defecit persists despite eye mvt o Therefore '''attentional defecit '''due to parietal lobe lesion What frame of reference must we assume is disrupted? - Critical evidence: o V1 is intact o Neglect persists despite eye mvts o Left is not retinocentric but rather defined relative to viewer - '''Viewer centered neglect: person’s midline ' - Difficulty in processing 'contralesional '''side of midline regardless of eye position Neuropsych: half of each obj missing (group of bow is an obj) - Location defined with reference to '''represented object '(not retina or viewer): '''object-centered frame of ref - You’ll be able to see it when you flip the obj - What counts as an object? o Grouping/visual attributes - Locations defined relative to obj’s right and left side - Difficulty processing/perceiving stim of contralesional side of obj regardless of midline/eye pos Scene copy and gap detectionà viewer centered neglect associated with lesions to 'inferior lobule ' Superior temporal gyrus: object centerd neglect Monkey studies show: To grab mug, refrence frame must be in common frame of ref